The present invention pertains to methods and means for simultaneously joining together electrical and other components through the application of directed energy, such as ultrasonic energy. More particularly, the present invention is directed to electro/mechanical joint formation by the application of directed energy, typically ultrasonic energy, in order to simultaneously bond together polymer substrates and metal circuit patterns which are present as conductive coatings on separate substrates.
Ultrasonic bonding methods are used to permanently bond two or more parts made of a polymer material, particularly when or where it is undesirable to use adhesives. The use of adhesives can adversely effect the strength of the mechanical joint in instances where the joint is exposed to certain chemicals, solvents, pressures and temperatures. In addition, ultrasonic bonding requires little or no surface preparation, is very fast, can be readily automated, and no fixture or cure time is required for the parts after the process is complete.
Ultrasonic bonding of metals is also known. Permanent bonding obviates the need for mechanical fasteners such as screws, bolts or rivets as well as eliminating the need for other bonding methods such as brazing or soldering. Ultrasonic bonding of metals generally creates an improved electrical joint in that the interface between the two mating parts is essentially eliminated.
In certain applications, it is necessary or desired to provide a joint with both mechanically robust and electrically conductive characteristics. It would be desirable to take advantage of the unique features that ultrasonic bonding can provide, however, to date, it is not known how to achieve this on a conductively coated plastic part. Each bonding operation can be done separately, as described above; however, simultaneous bonding is difficult. One of the reasons for this is that for polymer to polymer ultrasonic bonding, the ultrasonic energy is applied to each part so that the movement of one part relative to the other is a direct impact motion (hammer type movement). However, with metal to metal ultrasonic bonding, the movement of one part relative to the other is sheer (one part sliding against the other). Accordingly, the desired direction of motion for bonding polymers and metals is different and seemingly incompatible.
Bonding of conductively coated polymer surfaces together is useful in many applications among which are, to name bit a few: (1) the sealing of housings for the control of electromagnetic interference (EMI); (2) the protection of electronic packages from electrostatic discharge (ESD) events; and (3) the affixation of surface mount components to thermoplastic circuit cards.